Fibrocartilaginous tissues are found throughout the musculoskeletal system in regions experiencing substantial levels of both tension and compression during functional loading. These tissues have highly organized, heterogeneous structures that are well suited for their mechanical functions. Like articular cartilage, fibrocartilage has a poor intrinsic repair capacity, and damage or degradation often leads to early osteoarthritis or joint dysfunction. Tissue engineering offers the potential to treat damaged or diseased fibrocartilages with biologically and mechanically functional replacements. In order for such an approach to be successful, however, strategies must be developed that ultimately produce an engineered replacement with cell phenotypes and ECM organization capable of surviving and functioning in the complex and demanding mechanical environment of the native tissue. Taking cues from fibrocartilage development, we believe that coordinated manipulation of the biochemical and biomechanical environment can be employed as part of a strategy to guide the formation of fibrocartilage replacements with appropriate cell and matrix constituents. Specifically, we propose that oscillatory compression will act as a chondrogenic stimulus while oscillatory tension will act as a fibrogenic stimulus, and that each is capable of modulating MSC differentiation. Combinations of these mechanical stimuli with specific biochemical factors promoting chondrogenic or fibrogenic differentiation will produce a range of cell phenotypes characteristic of fibroblasts, chondrocytes, and fibrochondrocytes. The following three hypotheses will be tested: 1) Short duration oscillatory compression and tension will differentially modulate cellular activity of differentiating human MSCs. 2) Sustained oscillatory compression and tension will differentially alter human MSC differentiation, construct composition and mechanical properties. 3) Effects of mechanical stimulation on human MSCs will persist without lineage-specific mechanical or biochemical stimulation. Successful completion of this proposal will provide a fundamental understanding of the role for tension and compression in guiding human MSC differentiation, and will allow the development of novel strategies involving spatially varying stimuli to produce engineered fibrocartilage replacements controlled spatial heterogeneity. PUBLIC HEALTH RELEVANCE: These studies will enhance our understanding of how mechanical loading influences the development of tissues such as cartilage and meniscus. This will aid in the development of functional tissue engineered replacements and may aid in understanding why particular approaches to cartilage repair succeed or fail.